Photoelectric relay devices



Dec. 13, 1960 F. A. RAYMOND 2,964,685

PHOTOELECTRIC RELAY DEVICES Filed Oct, 25, 1957 ite ` atent nice 2,964,685 PHOTOELECTRIC RELAY DEVICES Francis Raymond, La Grange, Ill., assigner, by mesne assignments, to R. Hoe & Co., a corporation Filed Oct. 23, 1957, Ser. No, 691,984 9 Claims. (Cl. 317-124) My invention relates to photoelectric relay devices and, more particularly, to dark-light or on-off responsive devices that control an electromagnetic relay to switch from one to the other Contact position depending upon absence and presence of illumination at a photocell. Such devices are applicable for on-off controls of various kinds, for instance for the purpose of regulating the position of a travelling web of paper in printing plants where the web either obscures or exposes the photocell relative to a light source.

It is an object of my invention to provide a photoelectric relay device generally of the above-mentioned onoft type that combines utmost simplicity of circuitry with a minimum of co-mponents and secures reliable snapaction performance of the contact relay without requiring amplifiers or similar accessories.

Another object of my invention, conjointly with the one above mentioned, is to also eliminate the need for a stabilized voltage source or for voltage-regulating accessories while nevertheless affording reliable operation regardless of wide-range voltage fluctuations in the power supply of the device.

Further objects of the invention are to make a photoelectric relay device insensitive to intensity variations of the appertaining light source and insensitive to variations in ambient lighting.

To achieve these objects, and in accordance with a feature of my invention, I connect a resistor in series with one pole of a voltage source, preferably comprising a rectifier energized from an alternating-current line; and I connect two parallel branch circuits between the series resistor and the other pole of the voltage source, one branch circuit containing one coil and the other branch circuit the other coil of a differential electromagnetic relay whose movable contact will assume one or another position depending upon which of the two differentially coactive coils is more strongly excited at a time than the other. I further connect serially in one of the two branch circuits a photo-conductive cell which responds to absence and presence of illumination by exhibiting high dark-resistance and low light-resistance, a photoelectric semiconductor or crystal device, such as a cadmium-selenium (CdSe) cell, being preferably applicable. The second coil of the differential relay is connected in the other branch circuit in series with further resistor means whose resistance, preferably, is adjustable for Calibrating purposes.

According to another feature of the invention, I connect-a second photoelectric cell serially in the abovementioned other branch circuit and mount the second cell at or within the light-source assembly that provides illumination for the first-mentioned cell (main cell), so that intensity varia-tions of the light source will act on both cells and are compensated as regards their action upon the ditferential relay. t

According to a further feature, I connect an additional branch circuit parallel to the one containing the said other relay coil and provide the -additional branch circuit with another photoelectric cell which is mounted near the main cell but outside of the controlling beam of light so as to respond only to those ambient lighting conditions that may also affect the main cell, whereby variations in ambient lighting are also compensated as regards their effect upon the differential relay.

Relay devices embodying the above-mentioned features operate reliably without amplifiers to inherently produce snap action of the electromagnetic relays regardless of voltage fluctuations of the power source or various other variable conditions, as will be more fully understood from the schematic circuit diagrams of two embodiments of the invention illustrated by way of example in Figs. l and 2 respectively of the accompanying drawing and described presently.

In the following description of the device shown in Fig. 1, numerical parameter values of the illustrated components are mentioned in parentheses; but it should be understood that these values are given as examples only and may be modified, in proper correlation to one another, depending upon the requirements or desiderata of any particular application.

The relay device illustrated in Fig. 1 is energized at terminals 1 and Z from an alternating-current line (220 volts). Connected across terminals 1 and 2 is the midtapped primary winding 3 of a transformer 4. The secondary Winding 5 (6 volts) of the transformer energizes a lamp 6 which forms the light source for a photo-conductive cell 7, preferably a semiconductor or crystal-type cell having high resistance when dark and low resistance when illuminated from lamp 6 (CdSe cell: dark resistance virtually infinite, light resistance about 15,000 ohms). The mid-tap of transformer winding 3 and the terminal 2 are connected to the respective input terminals 8 and 9 of a full-wave rectifier bridge 10 (115 volts. 20 milliamps.) of the dry type, selenium or silicon rectifiers being well applicable for this purpose. Connected across the output terminals 11, 12 of rectifier 10 is a smoothing capacitor 13 (8 mfd., 150 volt D.C.). A resistor R1 (100,000 ohms, 1 watt) is connected to output terminal 11. Two branch circuits 15 and 16 extend in parallel from resistor R1 to the other output terminal 12 of rectitier 10.

The device is provided with a highly sensitive electromagnetic relay RY1 of the differential type. The relay has two interconnected magnet coils 17 and 18 (3900 ohms each) which cooperate differentially to actuate two relay contacts 19 and 20. When one or 'both relay coils are energized, either contact 19 or contact 20 is closed depending upon which of the two coils is more strongly excited than the other. If the relay is closed by hand with no power applied to the coils, the armature and contacts will retain the manually set position. This ensures snap action and prevents the danger of chattering when the current in both coils is nearly the same.

Relay coil 18 is connected in branch circuit 15 in series with the photoconductive cell 7. Relay coil 17 is connected in branch circuit 16 in series with a fixed resistor R2 (100,000 ohms, 1 watt) and a Calibrating rheostat R3 (total 500,000 ohms, 1 watt).

A power-operated control relay or contactor RY2 has its electromagnetic control coil 21 connected across the power supp-ly terminals 1 and 2 under control by contact 20 of relay RY1. When power relay RY2 is energized by the closing of contact 20, it closes a contact 2.2 and opens another contact 23 in order to thereby control the power supply to a current-consuming device or circuitry connected across terminal 24 and either one of terminals 25 and 26. The contact 19 in relay RY1 is available for similarly controlling some other device but is not used in the illustrated embodiment.

When terminals 1, 2 are energized and lamp 6 is in operation while cell 7 is obscured by an intervening object such as la web of paper, the cell 7 has a very high resistance and the dark-current then owing in branch circuit is zero or negligible. Hence, relay coil 18 is substantially de-energized. Under the same conditions, however, current fioWs through resistors R1, R2 and R3 and through coil 17. As a result, contact is kept in more fully open position; and contact 19, here not utilized, is closed. When the obscuring object is removed so that cell 7 receives illumination, its resistance drops. As a result, both circuit branches 15 and 16 are now conductive so that the total resistance in the load circuit of rectifier 10 is reduced. Hence more current will now flow through resistor R1. At the same time, the shunt connection across resistors R2 and R3 now effected by the active branch 15, reduces the current flow through resistors R2, R3 and coil 17 while applying full excitation to coil 18. Consequently, the excitation of coil 18 becomes by far predominant, and relay R1 switches contact 20 to closed position while contact 19 opens. The closing of contact 20 energizes the power-operated coil 21 of power relay R2 in order to effect the desired control operation.

The photoconductive semiconductor cell 7 exhibits a resistance inversely proportional to the intensity of the light falling upon it. The relative ratings of cell 7 and lamp 6 are such that cell 7 passes enough current for proper operation if the voltage at lamp 6 is below the rated lamp voltage. Assume for example, that cell 7 will sufficiently conduct when the lamp 6 is operated at 1.5 volts, but that normally the lamp receives much higher voltage. Then any variations in line voltage within a very wide range have no appreciable effect upon the on-off trigger action produced by obscuring or exposing the cell '7 relative to the light source. The justmentioned trigger action is augmented by the fact that the above-described double effect takes place simultaneously and instantaneously when the illuminating conditions of cell 7 are changed. That is, at the moment when cell 7 becomes illuminated, there is not only a considerable increase in the total amount of current drawn from the power source, but there is also a reduction in current fiow through the previously excited coil 17 accompanied by sudden application of full excitation voltage to the other coil 18. The resultant trigger effect upon the contact assembly of relay RY1, and also on the contacts of relay RY2, exhibits a rapid snap action despite the fact that no mechanical snap-action means are necessary.

`Any line-voltage fluctuation at terminals 1, 2 remains ineffective, over an extremely wide range, to disturb the above-described reliability of relay operation. This is so not only because of the above-mentioned insensitivity in the performance of cell 7, but also because of several other factors. In the first place, a voltage change causes the current in both coils 17, 18 to vary in step and since the relay RY1 can operate only on a difference of current in the coils, no transfer of the contacts 19, 20 results. A further stabilizing effect is produced by the fact that, on a line-voltage change, lamp 6 causes a change in the cell 7 current. This in turn causes a change in the IR-drop of resistor R1 which reflects such change into both coils 17, 18. While this is not an absolute form of regulation, it suffices to make the unit applicable where larger than usual voltage changes occur. For example, a relay device as described above, containing electric components whose parameter values `are those mentioned above in parentheses, was found to reliably operate even if the normal line voltage of 220 volt varies down to 110 volt or up to 330 volt. It will be recognized that these results are achieved Without utilizing any voltage stabilizing means or amplifying devices other than -those inherent in the circuit connections themselves,`thus resulting in a photo-electric relayrdevice of utmost simplicity and improved reliability of operation.

The embodiment illustrated in Fig. 2 is generally similar to the device shown in Fig. l and affords the same advantages but is modified toward further improved dependability in the event of certain lighting irregularities.

The relay device according to Fig. 2 is energized at terminals 31 and 32 from an alternating-current line. The two primary windings 33 and 34 of a power transformer 3S are connected in parallel across terminals 31, 32. The secondary winding 36 of transformer 35 normally energizes the lamp 37 of a light source through the control coil 38 of an auxiliary relay with two normally closed contacts 39 and 4f). Contact 39 controls a stand-by lamp 41 of the same light source, and contact 4f) controls an indicator lamp 42 or other signal. The light source, as is conventional for such purposes and hence not illustrated, comprises a housing and an optical lens system through which an illuminating beam of light is issued when either lamp 37 or lamp 41 is lit. It will be understood that the two lamps may be substituted by a single two-filament lamp. As long as lamp or filament 37 is in operation, the lamp or filament 41 is not energized. When lamp or filament 37 burns out, the stand-by 41 is immediately put in operation and the necessity for replacement is indicated by signal 42.

A rectifier bridge 43 is energized from terminals 31, 32 and has a smoothing capacitor 44 connected across its direct-current output terminals 45 and 46. A resistor R1 is connected in series between rectifier terminal 46 and a terminal point 47. A branch circuit 4S, which includes in series a photoconducting cell S1 as well as one coil 18 of a differential relay RY1, extends from resistor terminal 47 to rectifier terminal 45. Relay RY1 is identical with relay RY1 described above with reference to Fig. l and hence comprises a second coil 17 and two contacts 19, 20 which are normally in center position and open and of which one or the other closes depending upon the direction of the resultant differential excitation supplied to the two relay coils. Coil 17 is connected between rectifier terminal 45 and resistor terminal 47 through two parallel branch circuits 49 and 50. Branch circuit 49 includes in series a fixed resistor R2 and a calibrating rheostat R3 and, in this respect, corresponds to the circuit 16 of resistors R2 and R3 in Fig. l with the exception that another photoconducting cell S2 is connected in series with resistors R2 and R3. Cell S2is mounted Within the light-source assembly so as to be exposed to the light issuing from the source for illuminating the cell S1.

The second branch circuit 50 includes in series a third photoconducting cell S3 and a Calibrating rheostat R4. Cell S3 is mounted near cell S1 but outside of the beam of light coming from the light source so as to respond only to ambient light which may also affect cell S1. The three photo cells S1, S2, S3 are preferably all of the same type, consisting for instance of cadmium selenide cells of virtually infinite dark resistance but low light resistance as explained above with reference to cell 7 in Fig. l.

Disregarding at first the branch circuit '50 of cell S3, assume that lamp 37 is an operation but that the cell S1 is obscured by an intermediate object such as a web of paper. Under these conditions the cell S2 always receives full illumination, its resistance is low, and the branch circuit 49 is traversed by current which also flows through the resistor R1. Under these conditions, the operation of the relay device, generally, is the same as that of the device described with reference to Fig. 1. That is, the device operates sensitively to produce snap action of the relay RY1. When the intensity of the light coming from lamp 37 or 41 varies due to fluctuations vin line voltage, such variations are effectiveuponcell S2 and, when the cell S1 is exposed to the light beam, also upon the cell S1. Since these two cells are located in the two respective circuits of the differential relay coils 17 and 18, any resulting changes in current flow will thus cancel each other. Consequently, the device is greatly insensitive to changes in line voltage over an extremely wide range..

This range of voltage regulation is wider than in a relay device according to Fig. l. Cell S2, which is also caused to change its resistance due to changing lamp brilliancy, causes a change of current in coil 18. This offsets the change in current in coil 17, which was due to the change in resistance of cell S1. Since, normally, the current in both coils is approxi-mately fifty times as great as the current diferential required to cause the relay to operate, the only way the relay can transfer the contacts 19, 20 is by actually breaking the beam of light to cell S1. This differs considerably from conventional photo equipment in that it is not a threshold device.

Furthermore, by virtue of the above-mentioned compensating effect caused by the operation of cell S2, the occurrence of a false signal acting upon relay RY1 is prevented during the warm-up time of the light source, that is, when the source is iirst energized. Due to the same compensating operation, a false signal upon relay RY1 is also prevented when switching from one lamp or `filament of the light source to the other.

Turning now to the purpose of the branch circuit 50, it will be recognized that, since ambient light will equally act upon the cells S1 and S3, the effects of variations in ambient light will cancel and compensate each other relative to relay coils 17 and 18 because they occur simultaneously in differential related branch circuits 48 and 50. Consequently, the relay device is also insensitive to changes in ambient light conditions.

The relay RY1 in Fig. 2 is shown to have three leads T for connection to counting or measuring equipment or other devices, such as a power relay or contactor, to be controlled.

It will be obvious to those skilled in the art, upon a study of this disclosure, that the invention is not limited to the embodiments particularly illustrated and described herein, but permits of various modifications as regards individual components and circuitry, without departing from the essential features of my invention and within the scope of the claims annexed hereto.

I claim:

l. A photoelectric relay device, comprising a photoconducting cell having high dark-resistance and low light-resistance to respond to absence and presence of illumination, a voltage source having two terminals, a resistor connected to one of said terminals, two branch circuits extending parallel to each other between said resistor and said other terminal, a differential electromagnetic relay having two excitation coils and having contact means movable between open and closed positions depending upon the direction of the resultant differential excitation of said two coils, one of said coils being connected in one of said branch circuits in series with said cell so as to be substantially de-energized when said cell is dark, resistance means connected in said other branch circuit in series with said other coil to normally excite said other coil, whereby illumination of said cell causes increased current ow in said resistor but decreased current tlow in said other coil while simultaneously passing excitation current through said one coil to cause movement of said contact means from one to the other position.

2. A photoelectric relay device, comprising a photoconducting cell to respond to presence and absence of illumination, a voltage source, a resistor connected in series with said source, a differential relay having two differentially coactive coils and having normally open contact means, one of said coils being connected to said source in series with said cell and in series with said resistor whereby said one coil receives minimum excitation when said cell is dark, resistor means connected in series with said other coil across said series connection formed by said cell together with said one coil to normally supply current to said other coil for keeping said relay contact open, whereby illumination of said cell causes reduction of said current and simultaneous maximum excitation of said one coil to abruptly close said contact.

3. A photoelectric relay device, comprising a photoconducting cell, a light source for said cell, a power supply transformer having primary winding means for connection to a supply line and having a secondary winding connected to said light source and rated for normally operating said light source with a multiple of the voltage required for saturation of said cell, a rectier connected to said transformer to be energized therefrom and having direct-current output terminals, a resistor connected to one of said terminals, two branch circuits extending parallel to each other between said resistor and said other terminal, a differential electromagnetic relay having two excitation coils and having contact means movable between open and closed positions depending upon the direction of the resultant differential excitation of said two coils, one of said coils being connected in one of said branch circuits in series with said cell so as to be substantially de-energized when said cell is dark, resistance means connected in said other branch circuit in series with said other coil to normally excite said other coil, whereby illumination of said cell causes increased current flow in said resistor but decreased current How in said other coil while simultaneously passing excitation current through said one coil to cause movement of said contact means from one to the other position.

4. A photoelectric relay device, comprising a photoconducting cell, a light source for said cell, a power supply transformer having primary winding means for connection to a supply line and having a secondary winding connected to said light source and rated for normally operating said light source with a multiple of the voltage required for saturation of said cell, a rectifier connected to said primary winding to be energized therefrom and having direct-current output terminals, a resistor connected to one of said terminals, two branch circuits extending parallel to each other between said resistor and said other terminal, a differential electromagnet relay having two excitation coils and having contact means movable between open and closed positions in response to the direction of the resultant differential excitation of said two coils, one of said coils being connected in one of said branch circuits in series with said cell so as to be substantially de-energized when said cell is dark, resistance means connected in said other branch circuit in series with said other coil to normally excite said other coil, said resistance means comprising an adjustable Calibrating rheostat, whereby illumination of said cell causes increased current flow in said resistor but decreased current flow in said other coil while simultaneously passing excitation current through said one coil to cause movement of said contact means from one to the other position.

5. A photoelectric relay device, comprising a light source for issuing a beam of light, a photoelectric main cell mounted in the path of the beam to respond to being exposed and obscured relative to the beam, a voltage source having two terminals, a resistor connected to one of said terminals, two branch circuits extending parallel to each other between said resistor and said other terminal, a differential electromagnetic relay having two excitation coils and having contact means movable between open and closed positions depending upon the direction of the resultant differential excitation of said two coils, one of said coils being connected in one of said branch circuits in series with said main cell so as to be substantially de-energized when said main cell is obscured, ay

photoelectric auxiliary cell mounted at said light source to be continuously illuminated during operation of said light source, resistance means connected in said other branch circuit in series with said auxiliary cell and in series with said other coil to normally excite said other coil when said light source is in operation, whereby intensity uctuations of said light source are compensated relative to said relay and exposure of said main cell to the beam causes movement of said contact means from one to the other position.

6. A photoelectric relay device, comprising a light source for issuing a beam of light, a photoconducting main cell mounted in the beam path and having high dark-resistance and low light-resistance for response to being exposed and obscured relative to the beam, a voltage source having two terminals, a resistor connected to one of said terminals, two branch circuits extending parallel to each other between said resistor and said other terminal, a differential electromagnetic relay having two excitation coils and having contact means movable between open and closed positions depending upon the direction of the resultant dilerential excitation of said two coils, one of said coils being connected in one of said branch circuits in series with said main cell so as to be substantially de-energized when said main cell is obscured, a photoconducting auxiliary cell electrically similar to said main cell and mounted at said light source to be continuously illuminated during operation of said light source, adjustable resistance means connected in said other branch circuit in series with said auxiliary cell and in series with said other coil to normally excite said other coil when said light source is in operation, whereby intensity fluctuations of said llight source are compensated relative to said relay and exposure of said main cell to the beam causes movement of said contact means from one to the other position.

7. In a photoelectric relay device according to claim 5, said light source comprising two light-producing means having respective electric energizing circuits, a transfer relay having a coil connected in one of said energizing circuits and having a relay contact controlled by said coil and connected in said other energizing circuit for setting one of said means in operation when the other fails, whereby said auxiliary cell prevents faulty operation of said differential relay during transfer from one of said light-producing means to the other.

8. A photoelectric relay device according to claim 5, comprising a third photoelectric cell electrically similar to said main cell and connected in parallel with said resistance means and said auxiliary cell, said third cell being mounted outside the beam path but near said main cell so as to be subject to similar ambient lighting con ditions, whereby variations in ambient lighting are compensated relative to said differential relay.

9. A photoelectric relay device according to claim 5, comprising a third photoelectric cell and an adjustable resistor forming a series connection with each other, said series connection being connected in parallel with said resistance means and said auxiliary cell, said third cell being mounted outside the beam path but near said main cell so as to be subject to similar ambient lighting conditions, whereby Variations in ambient lighting are compensated relative to said differential relay.

References Cited in the le of this patent UNITED STATES PATENTS 1,721,216 Hardy et al July 16, 1929 2,065,758 Shepard Dec. 29, 1936 2,278,920 Evans et al. Apr. 7, 1942 2,353,218 Burnham et al July 1l, 1944 2,420,058 Sweet May 6, 1947 2,562,176 Curry July 31, 1951 2,721,297 IEstelle Oct. 18, 1955 

